Electro-optic displays, and materials and methods for production thereof

ABSTRACT

A sub-assembly useful in an electro-optic display includes a conductive layer and a layer of electro-optic medium. The conductive layer has a main section covered by the electro-optic medium, an exposed section free from the electro-optic medium, and a weak section connecting the main section and the exposed section, so that the exposed section can be manipulated to rupture the weak section, thus separating the exposed section from the main section without substantial damage.

REFERENCE TO RELATED APPLICATIONS

This application claims benefit of Provisional Applications Nos.60/946,997 and 60/947,001, both filed Jun. 29, 2007. This application isalso a continuation-in-part of application Ser. No. 11/682,409, filedMar. 6, 2007 (Publication No. 2007/0211331, now U.S. Pat. No.7,733,554), which itself claims benefit of Provisional Application No.60/767,171, filed Mar. 8, 2006.

This application is also related to:

(a) U.S. Pat. No. 6,982,178;

(b) application Ser. No. 10/605,024, filed Sep. 2, 2003 (Publication No.2004/0155857, now U.S. Pat. No. 7,561,324);

(c) U.S. Pat. No. 7,110,164;

(d) U.S. Pat. No. 7,075,703;

(e) application Ser. No. 11/550,114 filed Oct. 17, 2006 (Publication No.2007/0109219, now U.S. Pat. No. 7,839,564);

(f) application Ser. No. 11/612,732, filed Dec. 19, 2006 (PublicationNo. 2007/0152956, now U.S. Pat. No. 7,649,674); and

(g) application Ser. No. 11/850,831, filed Sep. 6, 2007 (Publication No.2008/0057252, now U.S. Pat. No. 7,583,427).

The entire contents of these patents and copending applications, and ofall other U.S. patents and published and copending applicationsmentioned below, are herein incorporated by reference.

BACKGROUND OF INVENTION

This invention relates to electro-optic displays, and to materials andmethods for the production and testing of such displays. This inventionis particularly, but not exclusively, intended for use with displayscomprising encapsulated electrophoretic media. However, the inventioncan also make use of various other types of electro-optic media whichare solid, in the sense that they have solid external surfaces, althoughthe media may, and often do, have internal cavities which contain afluid (either liquid or gas). Thus, the term “solid electro-opticdisplays”includes encapsulated electrophoretic displays, encapsulatedliquid crystal displays, and other types of displays discussed below.

Electro-optic displays comprise a layer of electro-optic material, aterm which is used herein in its conventional meaning in the imaging artto refer to a material having first and second display states differingin at least one optical property, the material being changed from itsfirst to its second display state by application of an electric field tothe material. Although the optical property is typically colorperceptible to the human eye, it may be another optical property, suchas optical transmission, reflectance, luminescence or, in the case ofdisplays intended for machine reading, pseudo-color in the sense of achange in reflectance of electromagnetic wavelengths outside the visiblerange.

The terms “bistable” and “bistability” are used herein in theirconventional meaning in the art to refer to displays comprising displayelements having first and second display states differing in at leastone optical property, and such that after any given element has beendriven, by means of an addressing pulse of finite duration, to assumeeither its first or second display state, after the addressing pulse hasterminated, that state will persist for at least several times, forexample at least four times, the minimum duration of the addressingpulse required to change the state of the display element. It is shownin U.S. Pat. No. 7,170,670 that some particle-based electrophoreticdisplays capable of gray scale are stable not only in their extremeblack and white states but also in their intermediate gray states, andthe same is true of some other types of electro-optic displays. Thistype of display is properly called “multi-stable” rather than bistable,although for convenience the term “bistable” may be used herein to coverboth bistable and multi-stable displays.

Several types of electro-optic displays are known. One type ofelectro-optic display is a rotating bichromal member type as described,for example, in U.S. Pat. Nos. 5,808,783; 5,777,782; 5,760,761;6,054,071 6,055,091; 6,097,531; 6,128,124; 6,137,467; and 6,147,791(although this type of display is often referred to as a “rotatingbichromal ball” display, the term “rotating bichromal member” ispreferred as more accurate since in some of the patents mentioned abovethe rotating members are not spherical). Such a display uses a largenumber of small bodies (typically spherical or cylindrical) which havetwo or more sections with differing optical characteristics, and aninternal dipole. These bodies are suspended within liquid-filledvacuoles within a matrix, the vacuoles being filled with liquid so thatthe bodies are free to rotate. The appearance of the display is changedby applying an electric field thereto, thus rotating the bodies tovarious positions and varying which of the sections of the bodies isseen through a viewing surface. This type of electro-optic medium istypically bistable.

Another type of electro-optic display uses an electrochromic medium, forexample an electrochromic medium in the form of a nanochromic filmcomprising an electrode formed at least in part from a semi-conductingmetal oxide and a plurality of dye molecules capable of reversible colorchange attached to the electrode; see, for example O'Regan, B., et al.,Nature 1991, 353, 737; and Wood, D., Information Display, 18(3), 24(March 2002). See also Bach, U., et al., Adv. Mater., 2002, 14(11), 845.Nanochromic films of this type are also described, for example, in U.S.Pat. Nos. 6,301,038; 6,870,657; and 6,950,220. This type of medium isalso typically bistable.

Another type of electro-optic display is an electro-wetting displaydeveloped by Philips and described in Hayes, R. A., et al., “Video-SpeedElectronic Paper Based on Electrowetting”, Nature, 425, 383-385 (2003).It is shown in copending application Ser. No. 10/711,802, filed Oct. 6,2004 (Publication No. 2005/0151709), that such electro-wetting displayscan be made bistable.

One type of electro-optic display, which has been the subject of intenseresearch and development for a number of years, is the particle-basedelectrophoretic display, in which a plurality of charged particles movethrough a fluid under the influence of an electric field.Electrophoretic displays can have attributes of good brightness andcontrast, wide viewing angles, state bistability, and low powerconsumption when compared with liquid crystal displays. Nevertheless,problems with the long-term image quality of these displays haveprevented their widespread usage. For example, particles that make upelectrophoretic displays tend to settle, resulting in inadequateservice-life for these displays.

As noted above, electrophoretic media require the presence of a fluid.In most prior art electrophoretic media, this fluid is a liquid, butelectrophoretic media can be produced using gaseous fluids; see, forexample, Kitamura, T., et al., “Electrical toner movement for electronicpaper-like display”, IDW Japan, 2001, Paper HCS1-1, and Yamaguchi, Y, etal., “Toner display using insulative particles chargedtriboelectrically”, IDW Japan, 2001, Paper AMD4-4). See also U.S. PatentPublication Nos. 2005/0259068, 2006/0087479, 2006/0087489, 2006/0087718,2006/0209008, 2006/0214906, 2006/0231401, 2006/0238488, 2006/0263927 andU.S. Pat. Nos. 7,321,459 and 7,236,291. Such gas-based electrophoreticmedia appear to be susceptible to the same types of problems due toparticle settling as liquid-based electrophoretic media, when the mediaare used in an orientation which permits such settling, for example in asign where the medium is disposed in a vertical plane. Indeed, particlesettling appears to be a more serious problem in gas-basedelectrophoretic media than in liquid-based ones, since the lowerviscosity of gaseous suspending fluids as compared with liquid onesallows more rapid settling of the electrophoretic particles.

Numerous patents and applications assigned to or in the names of theMassachusetts Institute of Technology (MIT) and E Ink Corporation haverecently been published describing encapsulated electrophoretic media.Such encapsulated media comprise numerous small capsules, each of whichitself comprises an internal phase containing electrophoretically-mobileparticles suspended in a liquid suspending medium, and a capsule wallsurrounding the internal phase. Typically, the capsules are themselvesheld within a polymeric binder to form a coherent layer positionedbetween two electrodes. Encapsulated media of this type are described,for example, in U.S. Pat. Nos. 5,930,026; 5,961,804; 6,017,584;6,067,185; 6,118,426; 6,120,588; 6,120,839; 6,124,851; 6,130,773;6,130,774; 6,172,798; 6,177,921; 6,232,950; 6,249,271; 6,252,564;6,262,706; 6,262,833; 6,300,932; 6,312,304; 6,312,971; 6,323,989;6,327,072; 6,376,828; 6,377,387; 6,392,785; 6,392,786; 6,413,790;6,422,687; 6,445,374; 6,445,489; 6,459,418; 6,473,072; 6,480,182;6,498,114; 6,504,524; 6,506,438; 6,512,354; 6,515,649; 6,518,949;6,521,489; 6,531,997; 6,535,197; 6,538,801; 6,545,291; 6,580,545;6,639,578; 6,652,075; 6,657,772; 6,664,944; 6,680,725; 6,683,333;6,704,133; 6,710,540; 6,721,083; 6,724,519; 6,727,881; 6,738,050;6,750,473; 6,753,999; 6,816,147; 6,819,471; 6,822,782; 6,825,068;6,825,829; 6,825,970; 6,831,769; 6,839,158; 6,842,167; 6,842,279;6,842,657; 6,864,875; 6,865,010; 6,866,760; 6,870,661; 6,900,851;6,922,276; 6,950,200; 6,958,848; 6,967,640; 6,982,178; 6,987,603;6,995,550; 7,002,728; 7,012,600; 7,012,735; 7,023,420; 7,030,412;7,030,854; 7,034,783; 7,038,655; 7,061,663; 7,071,913; 7,075,502;7,075,703; 7,079,305; 7,106,296; 7,109,968; 7,110,163; 7,110,164;7,116,318; 7,116,466; 7,119,759; 7,119,772; 7,148,128; 7,167,155;7,170,670; 7,173,752; 7,176,880; 7,180,649; 7,190,008; 7,193,625;7,202,847; 7,202,991; 7,206,119; 7,223,672; 7,230,750; 7,230,751;7,236,790; 7,236,792; 7,242,513; 7,247,379; 7,256,766; 7,259,744;7,280,094; 7,304,634; 7,304,787; 7,312,784; 7,312,794; 7,312,916;7,237,511; 7,339,715; 7,349,148; 7,352,353; 7,365,394; and 7,365,733;and U.S. Patent Applications Publication Nos. 2002/0060321;2002/0090980; 2003/0102858; 2003/0151702; 2003/0222315; 2004/0105036;2004/0112750; 2004/0119681; 2004/0155857; 2004/0180476; 2004/0190114;2004/0257635; 2004/0263947; 2005/0000813; 2005/0007336; 2005/0012980;2005/0018273; 2005/0024353; 2005/0062714; 2005/0099672; 2005/0122284;2005/0122306; 2005/0122563; 2005/0134554; 2005/0151709; 2005/0152018;2005/0156340; 2005/0179642; 2005/0190137; 2005/0212747; 2005/0253777;2005/0280626; 2006/0007527; 2006/0038772; 2006/0139308; 2006/0139310;2006/0139311; 2006/0176267; 2006/0181492; 2006/0181504; 2006/0194619;2006/0197737; 2006/0197738; 2006/0202949; 2006/0223282; 2006/0232531;2006/0245038; 2006/0262060; 2006/0279527; 2006/0291034; 2007/0035532;2007/0035808; 2007/0052757; 2007/0057908; 2007/0069247; 2007/0085818;2007/0091417; 2007/0091418; 2007/0109219; 2007/0128352; 2007/0146310;2007/0152956; 2007/0153361; 2007/0200795; 2007/0200874; 2007/0201124;2007/0207560; 2007/0211002; 2007/0211331; 2007/0223079; 2007/0247697;2007/0285385; 2007/0286975; 2007/0286975; 2008/0013155; 2008/0013156;2008/0023332; 2008/0024429; 2008/0024482; 2008/0030832; 2008/0043318;2008/0048969; 2008/0048970; 2008/0054879; 2008/0057252; and2008/0074730; and International Applications Publication Nos. WO00/38000; WO 00/36560; WO 00/67110; and WO 01/07961; and EuropeanPatents Nos. 1,099,207 B1; and 1,145,072 B1.

Many of the aforementioned patents and applications recognize that thewalls surrounding the discrete microcapsules in an encapsulatedelectrophoretic medium could be replaced by a continuous phase, thusproducing a so-called polymer-dispersed electrophoretic display, inwhich the electrophoretic medium comprises a plurality of discretedroplets of an electrophoretic fluid and a continuous phase of apolymeric material, and that the discrete droplets of electrophoreticfluid within such a polymer-dispersed electrophoretic display may beregarded as capsules or microcapsules even though no discrete capsulemembrane is associated with each individual droplet; see for example,the aforementioned U.S. Pat. No. 6,866,760. Accordingly, for purposes ofthe present application, such polymer-dispersed electrophoretic mediaare regarded as sub-species of encapsulated electrophoretic media.

A related type of electrophoretic display is a so-called “microcellelectrophoretic display”. In a microcell electrophoretic display, thecharged particles and the fluid are not encapsulated withinmicrocapsules but instead are retained within a plurality of cavitiesformed within a carrier medium, typically a polymeric film. See, forexample, U.S. Pat. Nos. 6,672,921 and 6,788,449, both assigned to SipixImaging, Inc.

Although electrophoretic media are often opaque (since, for example, inmany electrophoretic media, the particles substantially blocktransmission of visible light through the display) and operate in areflective mode, many electrophoretic displays can be made to operate ina so-called “shutter mode” in which one display state is substantiallyopaque and one is light-transmissive. See, for example, theaforementioned U.S. Pat. Nos. 6,130,774 and 6,172,798, and U.S. Pat.Nos. 5,872,552; 6,144,361; 6,271,823; 6,225,971; and 6,184,856.Dielectrophoretic displays, which are similar to electrophoreticdisplays but rely upon variations in electric field strength, canoperate in a similar mode; see U.S. Pat. No. 4,418,346. Other types ofelectro-optic displays may also be capable of operating in shutter mode.

An encapsulated electrophoretic display typically does not suffer fromthe clustering and settling failure mode of traditional electrophoreticdevices and provides further advantages, such as the ability to print orcoat the display on a wide variety of flexible and rigid substrates.(Use of the word “printing” is intended to include all forms of printingand coating, including, but without limitation: pre-metered coatingssuch as patch die coating, slot or extrusion coating, slide or cascadecoating, curtain coating; roll coating such as knife over roll coating,forward and reverse roll coating; gravure coating; dip coating; spraycoating; meniscus coating; spin coating; brush coating; air knifecoating; silk screen printing processes; electrostatic printingprocesses; thermal printing processes; ink jet printing processes;electrophoretic deposition (See U.S. Pat. No. 7,339,715); and othersimilar techniques.) Thus, the resulting display can be flexible.Further, because the display medium can be printed (using a variety ofmethods), the display itself can be made inexpensively.

Other types of electro-optic materials may also be used in the presentinvention.

An electrophoretic display normally comprises a layer of electrophoreticmaterial and at least two other layers disposed on opposed sides of theelectrophoretic material, one of these two layers being an electrodelayer. In most such displays both the layers are electrode layers, andone or both of the electrode layers are patterned to define the pixelsof the display. For example, one electrode layer may be patterned intoelongate row electrodes and the other into elongate column electrodesrunning at right angles to the row electrodes, the pixels being definedby the intersections of the row and column electrodes. Alternatively,and more commonly, one electrode layer has the form of a singlecontinuous electrode and the other electrode layer is patterned into amatrix of pixel electrodes, each of which defines one pixel of thedisplay. In another type of electrophoretic display, which is intendedfor use with a stylus, print head or similar movable electrode separatefrom the display, only one of the layers adjacent the electrophoreticlayer comprises an electrode, the layer on the opposed side of theelectrophoretic layer typically being a protective layer intended toprevent the movable electrode damaging the electrophoretic layer.

The manufacture of a three-layer electro-optic display normally involvesat least one lamination operation. For example, in several of theaforementioned MIT and E Ink patents and applications, there isdescribed a process for manufacturing an encapsulated electrophoreticdisplay in which an encapsulated electrophoretic medium comprisingcapsules in a binder is coated on to a flexible substrate comprisingindium tin oxide (ITO) or a similar conductive coating (which acts as anone electrode of the final display) on a plastic film, thecapsules/binder coating being dried to form a coherent layer of theelectrophoretic medium firmly adhered to the substrate. Separately, abackplane, containing an array of pixel electrodes and an appropriatearrangement of conductors to connect the pixel electrodes to drivecircuitry, is prepared. To form the final display, the substrate havingthe capsule/binder layer thereon is laminated to the backplane using alamination adhesive. (A very similar process can be used to prepare anelectrophoretic display usable with a stylus or similar movableelectrode by replacing the backplane with a simple protective layer,such as a plastic film, over which the stylus or other movable electrodecan slide.) In one preferred form of such a process, the backplane isitself flexible and is prepared by printing the pixel electrodes andconductors on a plastic film or other flexible substrate. The obviouslamination technique for mass production of displays by this process isroll lamination using a lamination adhesive. Similar manufacturingtechniques can be used with other types of electro-optic displays. Forexample, a microcell electrophoretic medium or a rotating bichromalmember medium may be laminated to a backplane in substantially the samemanner as an encapsulated electrophoretic medium.

As discussed in the aforementioned U.S. Pat. No. 6,982,178, (see column3, lines 63 to column 5, line 46) many of the components used in solidelectro-optic displays, and the methods used to manufacture suchdisplays, are derived from technology used in liquid crystal displays(LCD's), which are of course also electro-optic displays, though using aliquid rather than a solid medium. For example, solid electro-opticdisplays may make use of an active matrix backplane comprising an arrayof transistors or diodes and a corresponding array of pixel electrodes,and a “continuous” front electrode (in the sense of an electrode whichextends over multiple pixels and typically the whole display) on atransparent substrate, these components being essentially the same as inLCD's. However, the methods used for assembling LCD's cannot be usedwith solid electro-optic displays. LCD's are normally assembled byforming the backplane and front electrode on separate glass substrates,then adhesively securing these components together leaving a smallaperture between them, placing the resultant assembly under vacuum, andimmersing the assembly in a bath of the liquid crystal, so that theliquid crystal flows through the aperture between the backplane and thefront electrode. Finally, with the liquid crystal in place, the apertureis sealed to provide the final display.

This LCD assembly process cannot readily be transferred to solidelectro-optic displays. Because the electro-optic material is solid, itmust be present between the backplane and the front electrode beforethese two integers are secured to each other. Furthermore, in contrastto a liquid crystal material, which is simply placed between the frontelectrode and the backplane without being attached to either, a solidelectro-optic medium normally needs to be secured to both; in most casesthe solid electro-optic medium is formed on the front electrode, sincethis is generally easier than forming the medium on thecircuitry-containing backplane, and the front electrode/electro-opticmedium combination is then laminated to the backplane, typically bycovering the entire surface of the electro-optic medium with an adhesiveand laminating under heat, pressure and possibly vacuum. Accordingly,most prior art methods for final lamination of solid electrophoreticdisplays are essentially batch methods in which (typically) theelectro-optic medium, a lamination adhesive and a backplane are broughttogether immediately prior to final assembly, and it is desirable toprovide methods better adapted for mass production.

Electro-optic displays are often costly; for example, the cost of thecolor LCD found in a portable computer is typically a substantialfraction of the entire cost of the computer. As the use of electro-opticdisplays spreads to devices, such as cellular telephones and personaldigital assistants (PDA's), much less costly than portable computers,there is great pressure to reduce the costs of such displays. Theability to form layers of some solid electro-optic media by printingtechniques on flexible substrates, as discussed above, opens up thepossibility of reducing the cost of electro-optic components of displaysby using mass production techniques such as roll-to-roll coating usingcommercial equipment used for the production of coated papers, polymericfilms and similar media.

The aforementioned U.S. Pat. No. 6,982,178 describes a method ofassembling a solid electro-optic display (including an encapsulatedelectrophoretic display) which is well adapted for mass production.Essentially, this patent describes a so-called “front plane laminate”(“FPL”) which comprises, in order, a light-transmissiveelectrically-conductive layer; a layer of a solid electro-optic mediumin electrical contact with the electrically-conductive layer; anadhesive layer; and a release sheet. Typically, the light-transmissiveelectrically-conductive layer will be carried on a light-transmissivesubstrate, which is preferably flexible, in the sense that the substratecan be manually wrapped around a drum (say) 10 inches (254 mm) indiameter without permanent deformation. The term “light-transmissive” isused in this patent and herein to mean that the layer thus designatedtransmits sufficient light to enable an observer, looking through thatlayer, to observe the change in display states of the electro-opticmedium, which will normally be viewed through theelectrically-conductive layer and adjacent substrate (if present); incases where the electro-optic medium displays a change in reflectivityat non-visible wavelengths, the term “light-transmissive” should ofcourse be interpreted to refer to transmission of the relevantnon-visible wavelengths. The substrate will typically be a polymericfilm, and will normally have a thickness in the range of about 1 toabout 25 mil (25 to 634 μm), preferably about 2 to about 10 mil (51 to254 μm). The electrically-conductive layer is conveniently a thin metalor metal oxide layer of, for example, aluminum or ITO, or may be aconductive polymer. Poly(ethylene terephthalate) (PET) films coated withaluminum or ITO are available commercially, for example as “aluminizedMylar” (“Mylar” is a Registered Trade Mark) from E.I. du Pont de Nemours& Company, Wilmington Del., and such commercial materials may be usedwith good results in the front plane laminate. When a very flexiblefront plane laminate is desired for use in a flexible display,ITO-coated polymeric films having thicknesses of about 0.5 to 1 mil (13to 25 μm) are commercially available and can be coated withelectro-optic material.

The aforementioned U.S. Pat. No. 6,982,178 also describes a first methodfor testing the electro-optic medium in a front plane laminate prior toincorporation of the front plane laminate into a display. In thistesting method, the release sheet is provided with an electricallyconductive layer, and a voltage sufficient to change the optical stateof the electro-optic medium is applied between this electricallyconductive layer and the electrically conductive layer on the opposedside of the electro-optic medium. Observation of the electro-opticmedium will then reveal any faults in the medium, thus avoidinglaminating faulty electro-optic medium into a display, with theresultant cost of scrapping the entire display, not merely the faultyfront plane laminate.

The aforementioned U.S. Pat. No. 6,982,178 also describes a secondmethod for testing the electro-optic medium in a front plane laminate byplacing an electrostatic charge on the release sheet, thus forming animage on the electro-optic medium. This image is then observed in thesame way as before to detect any faults in the electro-optic medium.

Assembly of an electro-optic display using such a front plane laminatemay be effected by removing the release sheet from the front planelaminate and contacting the adhesive layer with the backplane underconditions effective to cause the adhesive layer to adhere to thebackplane, thereby securing the adhesive layer, layer of electro-opticmedium and electrically-conductive layer to the backplane. This processis well-adapted to mass production since the front plane laminate may bemass produced, typically using roll-to-roll coating techniques, and thencut into pieces of any size needed for use with specific backplanes.

The aforementioned 2004/0155857 describes a so-called “double releasefilm” which is essentially a simplified version of the front planelaminate of the aforementioned U.S. Pat. No. 6,982,178. One form of thedouble release sheet comprises a layer of a solid electro-optic mediumsandwiched between two adhesive layers, one or both of the adhesivelayers being covered by a release sheet. Another form of the doublerelease sheet comprises a layer of a solid electro-optic mediumsandwiched between two release sheets. Both forms of the double releasefilm are intended for use in a process generally similar to the processfor assembling an electro-optic display from a front plane laminatealready described, but involving two separate laminations; typically, ina first lamination the double release sheet is laminated to a frontelectrode to form a front sub-assembly, and then in a second laminationthe front sub-assembly is laminated to a backplane to form the finaldisplay, although the order of these two laminations could be reversedif desired.

The aforementioned 2007/0109219 describes a so-called “inverted frontplane laminate”, which is a variant of the front plane laminatedescribed in the aforementioned U.S. Pat. No. 6,982,178. This invertedfront plane laminate comprises, in order, at least one of alight-transmissive protective layer and a light-transmissiveelectrically-conductive layer; an adhesive layer; a layer of a solidelectro-optic medium; and a release sheet. This inverted front planelaminate is used to form an electro-optic display having a layer oflamination adhesive between the electro-optic layer and the frontelectrode or front substrate; a second, typically thin layer of adhesivemay or may not be present between the electro-optic layer and abackplane. Such electro-optic displays can combine good resolution withgood low temperature performance.

The aforementioned 2008/0057252 describes various methods designed forhigh volume manufacture of electro-optic displays using inverted frontplane laminates; preferred forms of these methods are “multi-up” methodsdesigned to allow lamination of components for a plurality ofelectro-optic displays at one time.

The aforementioned U.S. Pat. No. 6,982,178 also describes methods forforming an electrical connection between a backplane to which the frontplane laminate is laminated and the light-transmissiveelectrically-conductive layer within the front plane laminate. (Such aconnection is necessary because the electronic circuits which controlthe voltages applied to the pixel electrodes also normally control thevoltage applied to the front electrode.) As illustrated in FIGS. 21 and22 of this patent, the formation of the layer of electro-optic mediumwithin the front plane laminate may be controlled so as to leaveuncoated areas (“gutters”) where no electro-optic medium is present, andportions of these uncoated areas can later serve to form the necessaryelectrical connections. However, this method of forming connectionstends to be undesirable from a manufacturing point of view, since theplacement of the connections is of course a function of the backplanedesign, so that FPL coated with a specific arrangement of gutters canonly be used with one, or a limited range of backplanes, whereas foreconomic reasons it is desirable to produce only one form of FPL whichcan be used with any backplane.

Accordingly, the aforementioned U.S. Pat. No. 6,982,178 also describesmethods for forming the necessary electrical connections by coatingelectro-optic medium over the whole area of the FPL and then removingthe electro-optic medium where it is desired to form electricalconnections. However, such removal of electro-optic medium poses its ownproblems, especially when the FPL is formed by coating a thin (less thanabout 25 μm) polymeric film. Typically, the electro-optic medium must beremoved by the use of solvents or mechanical cleaning, either of whichmay result in damage to, or removal of, the electrically-conductivelayer of the FPL (this electrically-conductive layer usually being alayer of a metal oxide, for example indium tin oxide, less than 1 μmthick), causing a failed electrical connection. In extreme cases, damagemay also be caused to the front substrate (typically a polymeric film)which is used to support and mechanically protect the conductive layer.In some cases, the materials from which the electro-optic medium isformed may not be easily solvated, and it may not be possible to removethem without the use of aggressive solvents and/or high mechanicalpressures, either of which will exacerbate the aforementioned problems.

Similar methods using selective coating of electro-optic medium and/orselective removal of electro-optic medium may also be applied to thedouble release films and inverted front plane laminates discussed above.

It is common practice to use laser cutting to separate from a continuousweb of FPL pieces of appropriate sizes for lamination to individualbackplanes. Such laser cutting can also be used to prepare areas forelectrical connections to the backplane by “kiss cutting” the FPL withthe laser from the lamination adhesive side so that the laminationadhesive and electro-optic medium are removed from the connection areas,but the electrically-conductive layer is not removed. Such kiss cuttingrequires accurate control of both laser power and cutting speed if thethin and relatively fragile electrically-conductive layer is not to beremoved or damaged. Also, depending upon the location of the connection,bending of the electrically-conductive layer and the associated frontsubstrate may crack the conductive layer, resulting in failure to make aproper connection between the backplane and the conductive layer, andhence display failure.

The aforementioned 2007/0211331 describes methods of forming electricalconnections to the conductive layers of front plane laminates. Thisapplication describes a first process for the production of a frontplane laminate which comprises forming a sub-assembly comprising a layerof lamination adhesive and a layer of electro-optic medium; forming anaperture through this sub-assembly; and thereafter securing to theexposed surface of the lamination adhesive a light-transmissiveelectrode layer extending across the aperture. The resultant FPL has apre-cut aperture through the electro-optic medium and adhesive layers,this pre-cut aperture allowing contact to be made with the electrodelayer.

The aforementioned 2007/0211331 also describes a second process for theproduction of a front plane laminate which comprises forming asub-assembly comprising a layer of lamination adhesive and a layer ofelectro-optic medium; and thereafter securing to the exposed surface ofthe lamination adhesive a light-transmissive electrode layer, theelectrode layer having a tab portion which extends beyond the peripheryof the lamination adhesive and electro-optic layers.

One aspect of the present invention relates to alternative methods forforming electrical connections to the conductive layers of front planelaminates which are generally similar to those described in theaforementioned 2007/0211331 but which do not require forming an aperturethrough the electro-optic layer or the provision of a tab portion on theelectrode layer.

A second aspect of the present invention relates to reducing problemsexperienced in testing prior art front plane laminates and similarstructures. The first testing method for a front plane laminatedescribed in the aforementioned U.S. Pat. No. 6,982,178 obviouslyrequires that electrical contact be made with both thelight-transmissive electrically-conductive layer and the conductivelayer of the release sheet. Contact with the light-transmissiveelectrically-conductive layer (a so-called “top plane connection”) canbe made as described in the aforementioned 2007/0211331 by providing apre-cut aperture through the electro-optic medium and any adhesive layerlying between the electro-optic medium and the light-transmissiveelectrically-conductive layer. Contact with the conductive layer of therelease sheet may be achieved by providing a section of the releasesheet which extends outwardly beyond the remaining layers of the frontplane laminate, with the conductive layer being exposed on theextension.

A typical prior art front plane laminate (generally designated P100) ofthis type is illustrated in FIGS. 1 and 2 of the accompanying drawings,in which FIG. 1 is a top plan view of the front plane laminate and FIG.2 is a schematic section through one of the inspection tabs shown inFIG. 1. The FPL P100 has a main section P102, which is rectangular inshape and two inspection tabs each generally designated P104; each ofthe tabs P104 has an inner section P104A adjacent the main section P102and an outer section P104B.

As shown in FIG. 2, the FPL P100 comprises several different layers. Inorder from the top (viewing) surface of the FPL, these layers are:

-   -   (a) a masking film P106, which serves to protect the underlying        layers and is removed before the final display is placed in use;    -   (b) a layer of optically clear adhesive P108;    -   (c) a layer P110 of PET, which serves as a supporting and        protective layer supporting;    -   (d) a light-transmissive electrode layer P112 formed of        indium-tin-oxide (ITO);    -   (e) an electro-optic layer P114, illustrated as an encapsulated        electrophoretic layer;    -   (f) a lamination adhesive layer P116;    -   (g) a conductive aluminum coating P118 supported on;    -   (h) a polymer film P120 which, together with the aluminum        coating P118 forms a conductive release sheet.

All of the foregoing layers are present throughout the main section P102and in the inner section P104A of each tab P104. However, as shown inFIG. 2, only the aluminum coating P 118 and polymer film P 120 arepresent in the outer section P 104B of each tab P 104, so that in eachouter section P104 the upper surface (as illustrated in FIG. 2) of thealuminum coating is exposed to enable electrical contact to be made withthis coating. To enable contact to be made with the ITO layer P112, eachinner tab section P104A is provided with a top plane connection apertureP122, which extends from the lower surface (as illustrated in FIG. 2) ofthe FPL P100 through the polymeric layer P120, the aluminum coatingP118, the adhesive layer P116 and the electro-optic layer P114. Aprinted silver layer P124 covers the section of the ITO layer P112exposed by the aperture P122, this silver layer P124 serving to lessenthe risk of damage to the relatively fragile ITO layer P112 when a probeis used to make electrical contact with the ITO layer P112. (The silverlayer P124 is produced by printing silver ink on to the ITO layer P112supported on the PET layer P110 prior to coating the electro-optic layerP114 over the ITO layer 112.)

By contacting the exposed surfaces of the aluminum coating P118 and thesilver layer P124 with probes, the FPL P100, which is of a sizecorresponding to a single display, can be tested by the first testingmethod described in the aforementioned U.S. Pat. No. 6,982,178.Subsequent removal of the release sheet comprising the polymeric layerP120 and the aluminum coating P118 removes the outer tab section P104B,leaving the inner tab sections 104A and their apertures P122 availableto act as top plane connections in the final display.

The prior art FPL structure shown in FIGS. 1 and 2 gives good resultswith relatively thick FPL's, for example those described in theaforementioned U.S. Pat. No. 6,982,178 which are based upon a PET layerP110 having a thickness of about 5 mil (127 μm). However, when the priorart FPL structure shown in FIGS. 1 and 2 is based upon a PET layerhaving a thickness of about 1 mil (25 μm), there is a risk of mechanicaldamage to the aperture P122 or the adjacent parts of the silver layerP124 and ITO layer P112, and since in this structure the apertures P122are used both for testing purposes and as the top plane connections inthe final display, any damage to the apertures or the adjacentconductive layers during testing may affect the performance of the finaldisplay.

The structure shown in FIGS. 1 and 2 has other disadvantages. Asdescribed in the aforementioned U.S. Pat. No. 6,982,178, an FPL istypically prepared by coating the electro-optic layer on a polymericfilm already coated with ITO (such ITO-coated films are availablecommercially); if the silver layer P124 is present this layer is coatedbefore the electro-optic layer is applied. Separately, the adhesivelayer P116 is coated on to a conductive release sheet comprising thealuminum layer P118 and the polymeric layer P120, and the resultantadhesive-on-release sub-assembly is laminated, typically under heat andpressure, to the electro-optic layer. Desirably, up to this point theprocess is conducted on material in the form of webs or large sheets,and only after the FPL is prepared is it cut into pieces suitable foruse in forming individual displays.

If the structure shown in FIGS. 1 and 2 is prepared in this manner, itis either necessary to cut the electro-optic layer-on-PET andadhesive-on-release sheets separately before they are laminated togetherand then to laminate them keeping careful alignment to ensure that thealuminum layer remains exposed on the small outer tab sections P104B, orit is necessary to cut a piece of laminated FPL to the shape shown inFIG. 1, and then to remove the layers P106-P116 from the outer tabsections P104B. In either case, it is also necessary to form theapertures P122. In practice, the laminated FPL is cut to the shape shownin FIG. 1, and laser “kiss” cutting is applied from both sides of theFPL both to remove the unwanted layers from the outer tab sections P104Band to form the apertures 122. Such laser cutting may damage the silverlayer P124 and/or the adjacent part of the ITO layer P112, with thedisadvantageous results already noted.

Moreover, the structure shown in FIGS. 1 and 2 requires that the sametop plane connections (apertures P122) be used for both testing and inthe final display, whereas for engineering reasons it may be moreconvenient to provide separate sets of top plane connections for the twopurposes, and leaves the inner tab sections P104A remaining on the finalFPL after the conductive release sheet P118/P120 has been removed, andin some cases the presence of these protruding inner tab sections P104Amay be inconvenient.

The second aspect of the present invention seeks to provide a frontplane laminate, or similar article of manufacture, which reduces oreliminates the disadvantages of the prior art structure discussed above.

SUMMARY OF INVENTION

Accordingly, in one aspect this invention provides a process for theproduction of an article of manufacture useful in the production of anelectro-optic display, the process comprising:

-   -   providing an electro-optic sub-assembly comprising a layer of        electro-optic medium;    -   providing an adhesive sub-assembly comprising an adhesive layer,        the adhesive layer being larger in at least one dimension than        the layer of electro-optic medium, the adhesive layer having at        least one aperture extending therethrough; and    -   adhering the adhesive sub-assembly to the electro-optic        sub-assembly so that a part of the adhesive layer adheres to the        layer of electro-optic medium but the at least one aperture in        the adhesive layer is spaced from the layer of electro-optic        medium (i.e., so that the electro-optic medium does not block        the adjacent ends of the aperture(s) in the adhesive layer).

In such a “pre-formed aperture” process, the electro-optic sub-assemblymay comprise a light-transmissive electrically-conductive layer whichwill form a front electrode in the final display. Also, in such a case,the electro-optic sub-assembly will typically also comprise at least onesupporting or protective layer on the opposed side of theelectrically-conductive layer from the layer of electro-optic medium,the supporting or protective layer serving to support theelectrically-conductive layer and to protect it against mechanicaldamage. The supporting or protective layer may also serve otherfunctions, for example by acting as a barrier against water vapor and/orultra-violet radiation, and/or providing a desired surface texture. (Theelectro-optic medium is of course normally viewed from the side carryingthe electrically-conductive layer.) Alternatively, the electro-opticsub-assembly may comprise a second adhesive layer disposed on onesurface of the layer of electro-optic medium; the adhesive sub-assemblyis adhered to the surface of the layer of electro-optic medium notcovered by the second adhesive layer. The surface of the second adhesivelayer remote from the layer of electro-optic medium may be covered by arelease sheet. The electro-optic sub-assembly may also comprise arelease sheet covering the surface of the layer of electro-optic mediumto be adhered to the adhesive sub-assembly, this release sheet beingremoved from the layer of electro-optic medium before the layer ofelectro-optic medium is contacted with the adhesive sub-assembly.

The adhesive sub-assembly will typically comprise a release sheetcarrying the adhesive layer. It is not necessary that the at least oneaperture in the adhesive layer extend through the release sheet, buttypically the at least one aperture will do so, since it is usually mostconvenient to form the at least one aperture by cutting (for example, bylaser or die cutting) completely through the adhesive sub-assembly.

The electro-optic medium used in the process of the present inventionmay be any solid electro-optic medium of the types previously described.Thus, the electro-optic medium may be a rotating bichromal member orelectrochromic medium. The electro-optic medium may also be anelectrophoretic material comprising a plurality of electrically chargedparticles disposed in a fluid and capable of moving through the fluidunder the influence of an electric field. The electrically chargedparticles and the fluid may be confined within a plurality of capsulesor microcells. Alternatively, the electrophoretic material may be of thepolymer-dispersed type, with the electrically charged particles and thefluid present as a plurality of discrete droplets surrounded by acontinuous phase comprising a polymeric material. The fluid used may beliquid or gaseous.

This invention extends to the novel sub-assemblies and displays producedby the process of the present invention. Articles of manufacture andelectro-optic displays produced using the process of the presentinvention can be used in any of the applications in which electro-opticdisplays have previously been used. Accordingly, this invention extendsto an electronic book reader, portable computer, tablet computer,cellular telephone, smart card, sign, watch, shelf label or flash drivecomprising a display of the present invention, or produced using amethod or component of the present invention.

This invention also provides a sub-assembly useful in the production ofan electro-optic display, the sub-assembly comprising:

-   -   a layer of electro-optic medium; and    -   an adhesive layer larger in at least one dimension than the        layer of electro-optic medium, the adhesive layer having at        least one aperture extending therethrough;    -   a part of the adhesive layer adhering to the layer of        electro-optic medium but the at least one aperture in the        adhesive layer being spaced from the layer of electro-optic        medium.

In such a sub-assembly, a plurality of discrete areas of the layers ofelectro-optic medium may be disposed on a substrate, the discrete areasbeing separated by lands free from the electro-optic medium, and aplurality of apertures may pass through the adhesive layer, one end ofeach aperture terminating in one of the lands. The sub-assembly maycomprise a light-transmissive electrically-conductive layer disposed onthe surface of the layer of electro-optic medium remote from theadhesive layer.

The invention extends to an electro-optic display comprising theaforementioned sub-assembly and a backplane adhered to the adhesivelayer, the backplane comprising at least one first electrode disposedadjacent the layer of electro-optic medium and at least one secondelectrode spaced from the layer of electro-optic medium, the at leastone second electrode being in electrical contact with thelight-transmissive electrically-conductive layer via the at least oneaperture in the adhesive layer. This invention also extends to anelectronic book reader, portable computer, tablet computer, cellulartelephone, smart card, sign, watch, shelf label or flash drivecomprising such a display.

In a second main aspect, this invention provides an article ofmanufacture (a “detachable tab front plane laminate” or “DTFPL”) for usein the production of an electro-optic display, the article comprising aconductive layer and a layer of electro-optic medium, the conductivelayer having a main section covered by the layer of electro-opticmedium, an exposed section in at least part of which the conductivelayer is exposed free from the electro-optic medium, and a weak sectionconnecting the main section and the exposed section, such that theexposed section can be manipulated to cause rupture of the weak section,thereby separating the exposed section from the main section withoutsubstantial damage to the main section.

Typically, in the detachable tab front plane laminate of the presentinvention, all sections of the conductive layer will be supported on asupporting layer (for example, a polymeric film) and both the conductivelayer and supporting layer will have weak sections to enable the exposedsection of the conductive layer and the associated part of thesupporting layer to be detached from the main section of the conductivelayer and the associated part of the supporting layer. The supportinglayer may also serve other functions, for example by acting as a barrieragainst water vapor and/or ultra-violet radiation, and/or providing adesired surface texture.

Although the article provided by the present invention has been referredto above as a “detachable tab front plane laminate” and will primarilybe described below with reference to “full” front plane laminatessimilar to that shown in FIGS. 1 and 2, the present invention can beapplied to other structures having an electro-optic layer and aconductive layer. For example, the aforementioned 2004/0155857 describesa double release film comprising an electro-optic layer sandwichedbetween two release sheets, either or both of which can include aconductive layer for testing purposes. Such a double release film can beprovided with detachable tabs in accordance with the present invention.Similarly, in the type of FPL shown in FIG. 2, the conductive layer P118of the release sheet could be omitted and a detachable tab provided forthe conductive layer P112, and the FPL tested by the second methoddescribed in the aforementioned U.S. Pat. No. 6,982,178, with the staticcharge being applied to the polymeric layer P120.

As described above, typically a front plane laminate intended fortesting will have two separate conductive layers, one conductive layer(P112 in FIG. 2) being that which will form the front electrode in thefinal display, and the other conductive layer (P118 in FIG. 2) beingpart of a conductive release sheet which will be removed from the frontplane laminate before lamination to a backplane. Desirably, in such adual conductive layer front plane laminate, a detachable exposed sectionis provided for each conductive layer. In order to facilitate removal ofthe two separate detachable exposed sections, they are desirably offsetfrom one another, i.e., spaced from one another in the plane of thelayer of electro-optic medium. The exposed section of the frontelectrode conductive layer may be provided as illustrated in the sameway as in FIG. 2, that is to say by providing an aperture extendingthrough layers of the front plane laminate (and the conductive releasesheet, if the conductive release sheet covers the location of theaperture) overlying the front electrode conductive layer. As in FIG. 2,the portion of the front electrode conductive layer exposed by theaperture may be strengthened by providing a conductive pad in electricalcontact with the conductive layer. Although the exposed sections of thetwo conductive layers could reside on the same detachable tab, it willtypically be convenient to provide two separate detachable tabs for theexposed sections of the two conductive layers. As discussed in moredetail below, providing separate tabs has the advantage that, at leastin some cases, the exposed section of the conductive layer on therelease sheet can be provided simply by weakening the appropriate areaof the FPL and then removing from the relevant tab the front substrate,with the electro-optic medium and adhesive attached thereto.

The weak section or sections of the DTFPL may have various forms,although it is of course necessary to preserve some electricalconnection between the exposed and main sections of the conductive layerto ensure that the electro-optic medium can still be switched during thetesting process. For example, in the type of FPL shown in FIG. 2 thethicknesses of the PET layer P110 and the polymeric layer P120 could bereduced, such as by contacting these layers with heated members.However, it is generally preferred that parts of the weak section becut, for example by perforating or rouletting; the latter may bepreferred since it does not generate numerous small pieces of debris.

The electro-optic medium used in the DTFPL of the present invention maybe any solid electro-optic medium of the types previously described.Thus, the electro-optic medium may be a rotating bichromal member orelectrochromic medium. The electro-optic medium may also be anelectrophoretic material comprising a plurality of electrically chargedparticles disposed in a fluid and capable of moving through the fluidunder the influence of an electric field. The electrically chargedparticles and the fluid may be confined within a plurality of capsulesor microcells. Alternatively, the electrophoretic material may be of thepolymer-dispersed type, with the electrically charged particles and thefluid present as a plurality of discrete droplets surrounded by acontinuous phase comprising a polymeric material. The fluid used may beliquid or gaseous.

Electro-optic displays produced using the DTFPL of the present inventioncan be used in any of the applications in which electro-optic displayshave previously been used. Accordingly, this invention extends anelectronic book reader, portable computer, tablet computer, cellulartelephone, smart card, sign, watch, shelf label or flash drivecomprising a display produced using an article of the present invention.

Finally, this invention provides a process for testing a layer ofelectro-optic medium, the process comprising:

-   -   providing an article comprising a conductive layer and a layer        of electro-optic medium, the conductive layer having a main        section covered by the layer of electro-optic medium, an exposed        section in at least part of which the conductive layer is        exposed free from the electro-optic medium, and a weak section        connecting the main section and the exposed section;    -   applying a potential to the conductive layer sufficient to        change the optical state of the layer of electro-optic medium;    -   observing the appearance of the layer of electro-optic medium        following the change; and    -   thereafter, manipulating the exposed section to cause rupture of        the weak section, thereby separating the exposed section from        the main section without substantial damage to the main section.

In such a process, the article (DTFPL) may comprise first and secondconductive layers disposed on opposed sides of the layer ofelectro-optic medium, each of the first and second conductive layersbeing provided with an exposed section and a weak section, the potentialis applied between the first and second conductive layers, andthereafter both exposed sections are manipulated to cause rupture ofboth weak sections.

The accompanying drawings are not strictly to scale. In particular, forease of illustration, the thicknesses of the various layers are greatlyexaggerated relative to their lateral dimensions. The present inventionis well adapted for the production of thin, flexible electro-opticdisplays; typically, the sub-assemblies used in the processes describedbelow will have thicknesses of about 100 μm, and can be laminated toflexible backplanes of similar thickness.

BRIEF DESCRIPTION OF DRAWINGS

As already mentioned, FIG. 1 of the accompanying drawings is a top planview of a prior art front plane laminate having inspection tabs.

FIG. 2 is a schematic section through one of the inspection tabs of thefront plane laminate shown in FIG. 1.

FIGS. 3A to 3E are schematic sections through various stages in apre-formed aperture process of the present invention.

FIG. 4A is a schematic top plan view of the stage of the pre-formedaperture process shown in FIG. 3C.

FIG. 4B is a schematic top plan view of the stage of the pre-formedaperture process shown in FIG. 3E.

FIGS. 5A to 5C are schematic sections through various stages in theprocess used to convert the product of the process of FIGS. 3A to 3E toa finished display.

FIGS. 6A to 6E are schematic sections, similar to those of FIGS. 3A to3E respectively through various stages in a process for the productionof a detachable tab front plane laminate of the present invention.

FIGS. 7A and 7B are schematic top plan views of the stages of theprocess corresponding to FIGS. 6C and 6E respectively.

DETAILED DESCRIPTION

Before describing in detail various embodiments of the present inventionit is useful to set out certain definitions. The term “backplane” isused herein consistent with its conventional meaning in the art ofelectro-optic displays and in the aforementioned patents and publishedapplications, to mean a rigid or flexible material provided with one ormore electrodes. The backplane may also be provided with electronics foraddressing the display, or such electronics may be provided in a unitseparate from the backplane. In flexible displays (and the presentinvention is especially although not exclusively intended for use inflexible displays), it is highly desirable that the backplane providesufficient barrier properties to preventingress of moisture and othercontaminants through the non-viewing side of the display. If one or moreadditional layers need to be added to the backplane to reduce ingress ofmoisture and other contaminants, the barrier layers should be located asclosely as possible to the electro-optic layer so that little or no edgeprofile of low barrier materials is present between the front (discussedbelow) and rear barrier layers.

Reference will be made hereinafter to “loose” and “tight” releasesheets. These terms are used in their conventional meaning in the art toindicate the magnitude of the force necessary to peel the relevantrelease sheet from the layer with which it is in contact, a tightrelease sheet requiring more force than a loose release sheet. Inparticular, if a stack of layers has a tight release sheet on one sideand a loose release sheet on the other, it is possible to peel the looserelease sheet away from the stack without separating the tight releasesheet from the stack.

Some of the displays and sub-assemblies of the present invention containtwo separate adhesive layers. When necessary or desirable, the twoadhesive layers will be denoted as “front” and “rear” adhesive layers,these terms denoting the position of the relevant adhesive layer in thefinal display; the front adhesive layer is the adhesive layer lyingbetween the electro-optic medium and the viewing surface of the display,while the rear adhesive layer lies on the opposed side of theelectro-optic layer from the front adhesive layer. In the commonsituation where a display has a single front electrode between theelectro-optic layer and the viewing surface and a plurality of pixelelectrodes on the opposed side of the electro-optic layer, the frontadhesive layer lies between the electro-optic layer and the frontelectrode, while the rear adhesive layer lies between the electro-opticlayer and the pixel electrodes.

As indicated above, in one aspect the present invention provides a“pre-formed aperture” process for the production of a sub-assemblyuseful in the manufacture of an electro-optic display. In thispre-formed aperture process, separate electro-optic and adhesivesub-assemblies are formed, the former comprising at least a layer ofelectro-optic medium and the later at least an adhesive layer. Theadhesive layer has one or more apertures extending therethrough. The twosub-assemblies are adhered together so that a part of the adhesive layeradheres to the layer of electro-optic medium, but the electro-opticmedium does not block the aperture(s) in the adhesive layer.

As already indicated, the electro-optic sub-assembly used in thisprocess may comprise at least one electrode layer, most commonly asingle continuous front electrode extending across the entire display.Typically, the surface of the electro-optic sub-assembly remote from theadhesive sub-assembly will form the viewing surface through which anobserver views the display. As with the backplane, the electro-opticsub-assembly may provide barrier properties to preventingress ofmoisture and other contaminants through the viewing side of the display.If one or more additional layers need to be added to the sub-assembly toreduce ingress of moisture and other contaminants, the barrier layersshould be located as closely as possible to the electro-optic layer sothat little or no edge profile of low barrier materials is presentbetween the front and rear barrier layers. For more detailed discussionof such barrier layers, and other optional layers in the twosub-assemblies, see the aforementioned 2007/0109219 and 2007/0152956.

FIGS. 3A to 3E are schematic sections through various stages in apre-formed aperture process of the present invention. In the first stepof the process, an electro-optic medium is coated or otherwise depositedon to a tight release sheet 302 to form an electro-optic layer 304.Separately, a front adhesive layer 306 is coated on to a loose releasesheet 308. The two resulting sub-assemblies are then laminated to eachother with the adhesive layer 306 in contact with the electro-opticlayer 304 to produce the structure shown in FIG. 3A. These steps are asdescribed in the aforementioned U.S. Pat. No. 7,110,164, and theresulting assembly is a double release sheet as described in theaforementioned 2004/0155857.

In the second step of the process, the structure shown in FIG. 3A iskiss cut with the loose release 308 facing the cutter (typically a lasercutter), the kiss cutting being effected such that the loose releasesheet 308, the front adhesive layer 306 and the electro-optic layer 304are severed but the tight release sheet 302 is not. The continuousportions of the loose release sheet 308, the front adhesive layer 306and the electro-optic layer 304 are then removed, either manually ormechanically, thus leaving the structure shown in FIG. 3B, in whichthere extend upwardly from the tight release sheet 302 multiple “mesas”comprising the islands 318 of the loose release sheet and similarlysized areas 316 and 314 of the front adhesive layer and electro-opticlayer respectively. Each of these mesas will eventually form a separatedisplay. (In some cases, it may be possible to recycle the portions ofthe front adhesive layer and electro-optic layer removed with the looserelease sheet 308 in other small displays.)

The stages of the process described thus far will typically be carriedout either on continuous webs of material, or on large sheets ofmaterial sufficient to form several final displays. For ease ofillustration, FIG. 3B shows only two separate mesas but it will beappreciated that in practice a larger number of mesas will be present ona single large sheet or web. When the process is carried on a web, on aroll-to-roll basis, the webs used may include tractor feed holes formedalong the side edges of the web of material to serve as alignment holes.Alternatively, fiducial marks could be provided on the web and thesefiducial marks sensed optically to control the alignment of the webs.

In the next step, the remaining portions 318 of the loose release sheetare peeled from the structure shown in FIG. 3B and the remaining layersof the structure are laminated to a sheet of a front substrate 320. Thefront substrate 320 is a multi-layer structure including anindium-tin-oxide (ITO) layer which forms the front electrode of thefinal display. The front substrate may further comprise a removablemasking film, which can be removed before the final display is placed inuse.

The front substrate is designed to provide the front light-transmissiveelectrode for the final display. The front substrate 320 can alsoprovide the necessary mechanical support for this thin and relativelyfragile front electrode. In addition, the front substrate preferablyprovides all necessary water vapor and oxygen barriers, and ultra-violetabsorption properties, desirable to protect certain electro-opticlayers, especially electrophoretic layers. The front substrate may alsoprovide desirable anti-glare properties to the viewing surface of thefinal display. The front substrate 320 serves all of these functionswhile still being thin and flexible enough to enable the formation of afinal display sufficiently flexible to be wound around a mandrel of(say) 15 mm diameter. As already noted, the front substrate includes amasking film; this masking film is provided primarily to increase thethickness of the front substrate so as to facilitate handling of thissubstrate during laminations. In a preferred process, the totalthickness of the front substrate as it remains in the final display(i.e., with the masking film removed) is only about 1 mil (25 μm) andthe masking film is used to add about 2 mil (51 μm) to this thicknessfor ease of handling. The masking film also typically serves to preventscratching or adhesion of dust or debris to an adjacent anti-glare layerduring the laminations. The structure resulting from this step of theprocess is shown in FIG. 3C, and comprises an electro-optic sub-assemblysuitable for use in the process of the present invention.

The steps of the process described so far as essentially identical tothose of the process described with reference to FIGS. 2A to 2E of theaforementioned 2008/0057252, to which the reader is referred for furtherinformation.

At this point, a second, thin adhesive layer 322 is coated on to a thirdrelease sheet 324, and apertures 326 are formed though both the adhesivelayer 322 and the release sheet 324 at positions corresponding to wheretop plane connections (connections between the backplanes and the frontelectrodes) will be present in the final displays, thereby producing anadhesive sub-assembly suitable for use in the process of the presentinvention. To carry out the present process, the release sheet 302 ispeeled from the electro-optic sub-assembly shown in FIG. 3C and theadhesive layer 322 laminated to the electro-optic layer portions 314 togive the structure shown in FIG. 3D. Note that the apertures 326 in theadhesive layer are positioned so that they are spaced from the mesas(i.e., from the electro-optic portions 314) so that the mesas do notblock the apertures 326. FIG. 4A shows a top plan view corresponding toFIG. 3D but only illustrating a single mesa and its associated aperture326; at this stage of the process, the material is still in web or largesheet form and FIG. 4A illustrates only part of the web or sheet, asindicated by the curved boundary of front substrate 320 in FIG. 4A. (Forease of illustration, FIG. 4A shows only a single aperture 326associated with the mesa. In practice, it is usually desirable toprovide two or more apertures 326 associated with each mesa so as toprovide redundant top plane connections in each final display, therebyensuring that each display will still function correctly even if one ofits top plane connections is not correctly formed or becomes damagedduring use.)

The next stage of the process is singulation, that is to say separationof the portions of the sub-assembly corresponding to individualdisplays. The result of this singulation step is illustrated in FIGS. 3Eand 4B. The singulation step simultaneously effects three logicallyseparate operations, namely:

-   -   (a) cutting of the sheet or web into pieces of the size required        for individual displays;    -   (b) formation of apertures through the adhesive layer 322        required for mechanical alignment of the sub-assembly during        subsequent lamination to a backplane; and    -   (c) formation of an aperture through the front substrate 320,        the adhesive layers 322 and the release sheet 324, this aperture        being ultimately used to mount an electronic circuit device on        the backplane of the final display.

(For further discussion regarding operations (b) and (c), the reader isreferred to copending application Ser. No. 60/947,039, filed Jun. 29,2007.)

As illustrated in FIGS. 3E and 4B, operation (a) is effected by cuttingthe front substrate 320, the adhesive layer 322 and the release sheet324 along the same rectangular perimeter, thus defining a separate unit(piece) of front plane laminate which will eventually be laminated to abackplane to form a single display. In addition to the singulation ofthe separate unit of front plane laminate, this step creates an extendedtab or “tail” of non-optically active material (the portion of the frontplane laminate lying below the electro-optic layer 314 as illustrated inFIG. 4B) that adds to the thickness of the corresponding section of thefinal display. Were this tail of non-optically active material notpresent, the thickness of the final display in this region would be onlythe thickness of the backplane itself, and in thin, flexible displays,the thickness of this backplane may be only about 25 μm; the extendedtail section will typically provide an additional 25 μm of thickness,thus doubling the thickness of this region to about 50 μm. See theaforementioned 2007/0211331 for further discussion of providing a tab ortail portion of a front electrode layer, and use of such a tab or tailportion to provide electrical contact with the front electrode layer.

Operation (b) is effected by providing two small circular apertures 328adjacent one edge (the lower edge as illustrated in FIG. 4B) of therectangular front plane laminate. (For ease of comprehension, theapertures 328 are shown in broken lines in FIG. 3E even though FIG. 3Eis a section looking upwardly in FIG. 4B so the apertures 328 would notactually be visible in the section of FIG. 3E.) As shown in FIG. 3E, theapertures 328 lie within the tail section of the FPL and extend throughthe whole thickness of the FPL, passing through the front substrate 320,the adhesive layer 322 and the release sheet 324. The apertures 328 canbe used for mechanical alignment or attachment of the FPL duringlamination to a backplane or during later stages of manufacture. Asdescribed below with reference to FIGS. 5A to 5C, the apertures 328 canused to engage registration pins or similar co-operating membersprovided on the backplane, or on a substrate carrying the backplane, toensure accurate registration of the FPL with respect to the backplane.The apertures 328 can also be used in later stages of the manufacturingprocess to locate the final display module accurately with respect to ahousing or other surrounding portion (for example, a printed circuitboard) of the final commercial display unit, or to attach the displaymodule to such housing or surrounding portion.

Operation (c) is effected by providing a rectangular aperture 330 in thetail portion of the FPL, this rectangular aperture 330 extendingcompletely through the FPL, i.e., through the front substrate 320, theadhesive layer 322 and the release sheet 324. As discussed below, thetype of FPL shown in FIGS. 3E and 4B is typically used with a backplanewhich is essentially the same size as the FPL, so that the FPL coversessentially the whole of the backplane. Accordingly, if it is desired tohave electrical access to the backplane, for example for mounting driverchips on the backplane, an aperture must be formed to permit this, andthis is the function of the aperture 330. Driver chips or otherelectronic circuit devices can be placed within the aperture 330, andthe FPL surrounding the aperture provides a region of increasedthickness which assists ruggedization of the display.

FIG. 5A illustrates, in a highly schematic manner, a process in whichthe piece of front plane laminate shown in FIGS. 3E and 4B is laminatedto a backplane. As shown in FIG. 5A, a support table 350 is providedwith a pair of pins 352 (only one of which is visible in FIG. 5A). Abackplane 354 is provided with apertures which engage the pins 352. Therelease sheet 324 (see FIG. 3E) is removed from the front plane laminate356, which is then laid over the backplane with the apertures 328 (seeFIGS. 3E and 4B) engaged with the pins 352. A roller 358 passes over thefront plane laminate 356, thus adhering the adhesive layer 322 (see FIG.3E) to the adjacent surface of the backplane 354 and thus laminating thefront plane laminate to the backplane to form a display. As described inthe aforementioned U.S. Pat. No. 6,982,178, a conductive ink may beplaced on the backplane at appropriate points prior to this laminationso that during the lamination the conductive ink is forced into theapertures 326 to form conductive vias (not shown) connecting contactpads (also not shown) on the backplane to the electrode layer in thefront substrate 320. Alternatively, especially if the adhesive layer 322and the front substrate 320 are thin, the lamination will cause theelectrode layer in the front substrate 320 into electrical contact withone or more contact pads on the backplane without need for suchconductive ink. Following this lamination, the laminated FPL andbackplane are removed from the support table 350 as the structure shownin FIG. 5B. (The meaning of the arrows in FIG. 5B is explained below.)

When laminating front plane laminates to a backplane, the FPL musttypically be aligned with respect to backplane features, for examplecontact pads designed to provide contacts to the electrode layer presentin the front plane laminate. Depending on the design requirements, theFPL can be designed to be smaller than the backplane (to allow access toelectrical connections on areas of the backplane not covered by the FPL)or the same size as the backplane. If the FPL, or a barrier layerlaminated over the FPL, is the same size as the backplane, achieving aclean edge alignment can be difficult in practice, since there is alwayssome tendency for the FPL not to line up exactly with the backplane.Also, certain features desirable during manufacture, such as inspectiontabs or tacking strips, can be undesirable if present in the finisheddisplay module.

There is an increasing tendency to use electro-optic media with thinbackplanes based on polymeric films (for example, PET or poly(ethylenenaphthalate), PEN, available commercially under the Registered TradeMark TEONEX from DuPont Teijin Films of Hopewell Va.) or metal foils.Electro-optic displays based on such thin backplanes can be flexible orrollable and hence usable in certain applications (for example, a largedisplay screen capable of being stored in a cellular telephone—see theaforementioned 2002/0090980) where traditional displays cannot be used.It has now been found that an FPL laminated to such a polymeric or metalfoil backplane can readily be cut by industrial methods, for examplelaser cutting or die cutting, and that such cutting of an FPL/backplanelaminate enables an accurately matched edge to be achieved between theFPL (or a barrier layer overlying the FPL) and the backplane, withoutadverse effects on the functionality of the final display. Such cuttingalso allows for the removal of features useful during manufacture butnot wanted in the final display.

The laminate produced in FIG. 5B is then trimmed by laser or diecutting, as indicated schematically by the arrows in FIG. 5B to producethe final display module, illustrated schematically in FIG. 5C.

As mentioned above, the second main aspect of the present inventionrelates to a detachable tab front plane laminate comprising a conductivelayer and a layer of electro-optic medium, the conductive layer having amain section covered by the layer of electro-optic medium, an exposedsection in at least part of which the conductive layer is exposed freefrom the electro-optic medium, and a weak section connecting the mainsection and the exposed section, such that the exposed section can beseparated from the main section without substantial damage to the mainsection.

Typically, the surface of the DTFPL of the present invention whichremains exposed after lamination to a backplane will form the viewingsurface through which an observer views the display. As with thebackplane, a front substrate of the DTFPL may provide barrier propertiesto preventingress of moisture and other contaminants through the viewingside of the display. If one or more additional layers need to be addedto the DTFPL to reduce ingress of moisture and other contaminants, thebarrier layers should be located as closely as possible to theelectro-optic layer so that little or no edge profile of low barriermaterials is present between the front and rear barrier layers.

FIGS. 6A to 6E are schematic sections through various stages in theproduction of a DTFPL of the present invention. The process illustratedin FIGS. 6A to 6E closely resembles that illustrated in FIGS. 3A to 3Eabove, and accordingly the following description will be abbreviated todescribe only the aspects of the process of FIGS. 6A to 6E which differfrom the corresponding aspects of the process of FIGS. 3A to 3E. Thefirst two stages of the process, illustrated in FIGS. 6A and 6B areidentical to the corresponding stages shown in FIGS. 3A and 3Brespectively. The next stage, shown in FIG. 6C, is also in practiceidentical to that shown in FIG. 3C, but for reasons which will appearbelow, the front electrode layer 621, which will form thelight-transmissive electrode in the final display, is shown separatelyin FIG. 6C.

The next step of the process uses a third release sheet 624, one surfaceof which bears a conductive layer 625. As in the process illustrated inFIG. 3D, a thin adhesive layer 322 is coated on the third release sheet,but in this case the adhesive layer is deposited on the conductive layer625. Apertures 326 are formed through the adhesive layer 322, theconductive layer 625 and the release sheet 624 at positionscorresponding to where top plane connections will be present in thefinal displays. A second aperture 628 is also formed through theadhesive layer 322, the conductive layer 625 and the release sheet 624to allow the formation of a detachable inspection tab, as describedbelow. At the same time, the release sheet 624 is cut, preferablydiscontinuously, along a line 627 (see FIG. 7A) to form a tacking strip(discussed further below). The release sheet 302 is peeled from thestructure shown in FIG. 6C and the adhesive layer 322 laminated to theelectro-optic layer portions 314 to give the structure shown in FIG. 6D.FIG. 7A shows a corresponding top plan view which only illustrates asingle mesa and its associated apertures 326 and 628 and the line 627;at this stage of the process, the material is still in web or largesheet form and FIG. 7A illustrates only part of the web or sheet, asindicated by the curved boundary of front substrate 320 in FIG. 7A. (Forease of comprehension, the apertures 628 are shown in broken lines inFIGS. 6D and 6E even though FIGS. 6D and 6E are sections lookingupwardly in FIG. 7A so the apertures 628 would not actually be visiblein the sections of FIGS. 6D and 6E.) The adhesive layer 322 must ofcourse be correctly aligned with respect to the mesas to ensure that theapertures 326 and 628 and the line 627 are in the proper positionsrelative to their associated mesa, as shown in FIG. 7A. (For ease ofillustration, FIG. 7A shows only a single aperture 326 associated withthe mesa. In practice, as in the structure shown in FIG. 4A, it isusually desirable to provide two or more apertures 326 associated witheach mesa so as to provide redundant top plane connections in each finaldisplay, thereby ensuring that each display will still functioncorrectly even if one of its top plane connections is not correctlyformed or becomes damaged during use.)

The next stage of the process is singulation, that is to say separationof the portions of the FPL corresponding to individual displays. Theresult of this singulation step is illustrated in FIGS. 6E and 7B. Thesingulation not only severs the sheet or web into FPL pieces of the sizerequired for individual displays, but also forms detachable tabs 630 and632 on one edge (the lower edge as illustrated in FIG. 7B) of each FPLpiece. The tab 630 simply comprises a small rectangular area of the FPLseparated from the main part of the FPL by a rouletted (i.e.,discontinuously cut) line 634. The tab 632 surrounds the aperture 628and is separated from the main part of the FPL by a rouletted line 636.The discontinuous cuts along lines 634 and 636 extend completely throughthe FPL and are formed using the same laser cutter which separates theFPL piece shown in FIGS. 6E and 7B from the web. Since the discontinuouscuts do not completely sever the conductive layers 621 and 625, theportions of these conductive layers lying within the tabs 630 and 632are in electrical contact with the main portions of these conductivelayers in the major portion of the FPL piece.

The tab 630 is intended to provide access to the conductive layer 625 onthe release sheet 624, i.e., the tab 630 serves the same function as theouter tab sections P104B shown in FIGS. 1 and 2. Although as illustratedin FIGS. 6E and 7B, the conductive layer 625 is still covered by thefront substrate 320, the front conductive layer 621 and the adhesivelayer 322, it has been found that, by manually grasping the frontsubstrate 320 and pulling, the front substrate 320, the front conductivelayer 621 and the adhesive layer 322 will all part along line 634 toexpose the conductive layer 625. On the tab 632, the aperture 628exposes the front conductive layer 621, so that the tab 632 serves thesame function as the inner tab sections P104A shown in FIGS. 1 and 2.

To test the FPL piece shown in FIGS. 6E and 7B, the conductive layer 625on tab 630 is exposed as described in the preceding paragraph, andprobes are placed in contact with the conductive layer 625 on tab 630and the conductive layer 621 on tab 632. Varying voltages are applied tothe conductive layers 621 and 625, thus causing the electro-optic mediumto switch between its extreme optical states. The switching of theelectro-optic medium is observed either by eye or by a machine visionsystem. Once the electro-optic medium has been found satisfactory, theprobes are removed. The tabs 630 and 632 are then removed by manuallypulling on them, thus causing tearing along lines 634 and 636 andseparation of the tabs without damage to the main part of the FPL piece.Alternatively, the tab 630 could be used to peel the release sheet 624from the remaining layers of the FPL prior to lamination of the FPL to abackplane.

As also illustrated in FIG. 7B, the singulation of the FPL piece fromthe web results in the line 627 extending close to and parallel to oneedge of the FPL piece, so that between the line 627 and the adjacentedge is formed a tacking strip 629, in the form of an elongate arearunning along one edge of the FPL piece. Because the release sheet 624is severed along line 627, the section of the release sheet 624underlying the tacking strip 629 can be removed without removing therelease sheet 624 from the main part of the FPL piece. The tacking strip629 is provided to assist in locating the FPL piece on a backplane priorto the lamination of these two parts to form a display; the section ofthe release sheet 624 underlying the tacking strip 629 is removed andthe portion of the adhesive layer 322 thus exposed can be pressedmanually into the correct position for lamination to the backplane,before the main portion of the release sheet 624 is removed and thelamination operation completed.

It will be apparent to those skilled in the technology of electro-opticdisplays that numerous changes and modifications can be made in thepreferred embodiments of the present invention already described withoutdeparting from the scope of the invention. For example, in the preferredprocesses of the invention illustrated in the drawings, the invertedfront plane laminate is cut into pieces of the size required for anindividual display (see FIGS. 3E, 4B, 6E and 7B) before being laminatedto a backplane. When high volume production is desired, it may beconvenient to reverse the order of these singulation and laminationoperations, i.e., a sheet or web of inverted front plane laminatesufficient to form a plurality of displays could be laminated in analigned manner to a sheet or web of backplanes to form a plurality ofdisplays which are thereafter singulated from the sheet or web. In thecase where sheets of inverted front plane laminate and backplanes areused, the sheet of backplanes will typically be held on a support memberduring the lamination, and the singulation operation (and any desiredtrimming operation, such as that described above with reference to FIGS.5B and 5C) can be effected with the sheet of displays still held on thesupport member. Note that in this variant of the DTFPL process, it mayonly be necessary to provide a single pair of tabs 630, 632 to permittesting of the electro-optic medium of a complete sheet of FPL.

Also, in the preferred DTFPL process of the invention illustrated inFIGS. 6 and 7, the electro-optic medium does not extend into theremovable tabs. In other variants of the present invention, theelectro-optic medium may extend into part of the tab. For example, tabsused in DTFPL process may be similar to those illustrated in FIGS. 1 and2 but provided with weakened sections similar to those shown in FIG. 7Bso that they are detachable.

Furthermore, although the separable tabs used in the DTFPL process havebeen illustrated in the drawings as discrete rectangles protruding froma larger rectangular area which defines the form of the final piece ofFPL, it is not necessary that the tabs protrude in this manner.Depending upon the required form of the final piece FPL, the tabs couldfor example have the form of triangular sections disposed within thecorners of a rectangular piece of FPL, so that the final piece of FPLwould have the form of a rectangle with beveled corners.

Numerous other variants of the present invention are of course possible.Accordingly, the whole of the foregoing description is to be interpretedin an illustrative and not in a limitative sense.

1. An article of manufacture for use in the production of anelectro-optic display, the article comprising a conductive layer and alayer of electro-optic medium, the conductive layer having a mainsection covered by the layer of electro-optic medium, an exposed sectionin at least part of which the conductive layer is exposed free from theelectro-optic medium, and a weak section connecting the main section andthe exposed section, such that the exposed section can be manipulated tocause rupture of the weak section, thereby separating the exposedsection from the main section without substantial damage to the mainsection.
 2. An article of manufacture according to claim 1 furthercomprising a supporting layer disposed adjacent the conductive layer,the supporting layer having a main section disposed adjacent the mainsection of the conductive layer, an exposed section disposed adjacentthe exposed section of the conductive layer, and a weak section disposedadjacent the weak section of the conductive layer, such that the exposedsection of both the conductive layer and the supporting layer can bemanipulated to cause rupture of the weak sections thereof, therebyseparating the exposed sections of both the conductive layer and thesupporting layer from their respective main sections without substantialdamage to the main sections.
 3. An article of manufacture according toclaim 1 comprising first and second conductive layers disposed onopposed sides of the layer of electro-optic medium, each of the firstand second conductive layers being provided with an exposed section anda weak section.
 4. An article of manufacture according to claim 3wherein the exposed sections of the first and second conductive layerare spaced from one another in the plane of the layer of electro-opticmedium.
 5. An article of manufacture according to claim 1 wherein theweak section is formed by reducing the thickness of the conductivelayer.
 6. An article of manufacture according to claim 1 wherein theweak section is formed by perforating or rouletting.
 7. An article ofmanufacture according to claim 1 wherein the electro-optic medium is arotating bichromal member or electrochromic medium.
 8. An article ofmanufacture according to claim 1 wherein the electro-optic medium is anelectrophoretic material comprising a plurality of electrically chargedparticles disposed in a fluid and capable of moving through the fluidunder the influence of an electric field.
 9. An article of manufactureaccording to claim 8 wherein the electrically charged particles and thefluid are confined within a plurality of capsules or microcells.
 10. Anarticle of manufacture according to claim 8 wherein the electrophoreticmaterial is of the polymer-dispersed type, with the electrically chargedparticles and the fluid present as a plurality of discrete dropletssurrounded by a continuous phase comprising a polymeric material.
 11. Anarticle of manufacture according to claim 8 wherein the fluid isgaseous.
 12. A process for testing a layer of electro-optic medium, theprocess comprising: providing an article comprising a conductive layerand a layer of electro-optic medium, the conductive layer having a mainsection covered by the layer of electro-optic medium, an exposed sectionin at least part of which the conductive layer is exposed free from theelectro-optic medium, and a weak section connecting the main section andthe exposed section; applying a potential to the conductive layersufficient to change the optical state of the layer of electro-opticmedium; observing the appearance of the layer of electro-optic mediumfollowing the change; and thereafter, manipulating the exposed sectionto cause rupture of the weak section, thereby separating the exposedsection from the main section without substantial damage to the mainsection.
 13. A process according to claim 12 wherein the articlecomprises first and second conductive layers disposed on opposed sidesof the layer of electro-optic medium, each of the first and secondconductive layers being provided with an exposed section and a weaksection, the potential is applied between the first and secondconductive layers, and thereafter both exposed sections are manipulatedto cause rupture of both weak sections.